Atmospheric transport simulation of 210Pb and 7Be by the LMDz general circulation model and sensitivity to convection and scavenging parameterization

The atmospheric transport of 210Pb and 7Be is simulated by the Laboratoire de Météorologie Dynamique general circulation model, LMDz, driven by NCEP winds. Simulations are performed for one year (2006) in a regular grid with a resolution of 1.875° in longitude, 1.24° in latitude and 40 vertical levels. 210Pb and 7Be are two natural radionuclides attached to submicron aerosols and used as inert tracers to evaluate LMDz performance in terms of atmospheric transport, with particular emphasis on the tropics region. Daily averaged concentrations of both radionuclides are compared with available data, which are collected at surface stations with a 24 h sampling period.At tropical stations, time series of 7Be and 210Pb concentrations are not satisfactorily reproduced by the model using a traditional convection scheme. The purpose of this paper is to evaluate a more recently implemented convection scheme and two scavenging representations, in-cloud convective rainout and scavenging in convective updrafts. The former process associated to the new convection scheme, seems to be inappropriate in the tropics, since it tends to exaggerate the release of scavenged aerosols in the atmosphere due to re-evaporation of precipitation. Results suggest that scavenging of aerosols in updrafts could be sufficient to eliminate aerosols under convective regime.

Research Highlights
► Atmospheric transport of 210Pb and 7Be is simulated by a general circulation model.
► Daily-averaged concentrations are compared with data in the tropics.
► Sensitivity studies to the deep convection and to the scavenging schemes.
► Scavenging in updrafts is sufficient to eliminate aerosols under convective regime.